Someone refresh my memory... when did Marissa become a lesbian? Or was she bisexual and I just don't remember? lol

It just magically happened in the midst of the Summer when the show was canceled. After Bianca admitted her feelings for her, suddenly Marissa was like "Omg I have feelings for you too, Binx. Have for a while now but tried to ignore it <3 <3 <3" and they became a full on couple.